Epidemiological Evidence and Possible Mechanisms for the Association Between Cigarette Smoking and Injuries (Part 1).

Surveys indicated that 24% of military personnel are current cigarette smokers. Smoking is well known to increase the risk of cancers, cardiovascular and respiratory diseases, reproductive problems, and other medical maladies, but one of the little known effects of smoking is that on injuries. There is considerable evidence from a variety of sources that (1) smoking increases overall injury risk, (2) the greater the amount of smoking, the higher is the injury risk, and (3) smoking is an independent injury risk factor. Smoking not only affects the overall injury risk but also impairs healing processes following fractures (e.g., longer healing times, more nonunions, more complications), ligament injury (e.g., lower subjective function scores, greater joint laxity, lower subsequent physical activity, more infections), and wounding (e.g., delayed healing, more complications, less satisfying cosmetic results). Smoking may elicit effects on fractures through low bone mineral density (BMD), lower dietary intake of calcium and vitamin D, altered calcium metabolism, and effects on osteogenesis and sex hormones. Effects on wound healing may be mediated through altered neutrophils and monocytes functions resulting in reduced ability to fight infections and remove damaged tissue, reduced gene expression of cytokines important for tissue healing, and altered fibroblast function leading to lower density and amount of new tissue formation. Limited data suggest smoking cessation has favorable effects on various aspects of bone health over periods of 1 to 30 years. Favorable effects on neutrophil and monocyte functions may occur as early as 4 weeks, but fibroblast function and collagen metabolism (important for wound remodeling) appear to take considerably longer and may be dependent on the amount of prior smoking. Part 2 of this series will use this information to explore the possibility of a causal relationship between smoking and injuries.